The invention relates to towing aircraft on the ground, by means of towing devices designed to hitch the bottom portion of an undercarriage of the aircraft to a towing vehicle. Such towing devices are usually in the form of drawbars having one end mounted to the rear of a towing vehicle and the other end hitched to the bottom portion of the nose undercarriage of the aircraft. Generally, the drawbar is hitched to the undercarriage by inserting the end of the bar between lugs on the sliding rod of the nose undercarriage, close to the axle carrying the wheels of the undercarriage. The end of the drawbar is then secured thereto via a connecting pin referred to as a towing pin. The drawbar transmits high levels of traction and bending forces to the undercarriage, particularly when the aircraft is heavily loaded. The level of force transmitted to the undercarriage is also dependent on changes of direction imparted by the towing vehicle: the force threshold that can be supported by the undercarriage is much greater when the wheels of the undercarriage are substantially parallel to the longitudinal axis of the aircraft than when the wheels are oriented in a direction that is oblique relative to the longitudinal axis of the aircraft.
In order to avoid the drawbar damaging the undercarriage by transmitting forces that are too high thereto, it is known to use the towing pin as a mechanical fuse, by weakening it locally so that it breaks as soon as a predetermined force threshold is reached. Nevertheless, that solution is not without drawbacks. Firstly, in order to guarantee that the pin will break when the situation requires it, in particular when the steering angle of the wheels of the undercarriage is considerable, it is prudent to incorporate a large safety margin when determining its breaking threshold, which leads to pins breaking frequently, and sometimes unnecessarily. Secondly, breaking the pin does not constitute a response that is optimal in terms of safety, since even though it does indeed break the connection between the aircraft and the towing vehicle, thereby terminating the application of excessive forces to the undercarriage, it nevertheless does not necessarily cause the aircraft to come to rest immediately, so the aircraft is in danger of continuing to travel on the ground under its own momentum, as a result of inertia.